ankur Ji .u know I personally feel that if kid r taking much interest in mobiles the parents r also somewhere responsible for that. bcoz if we'll not show them it is interesting it is good .than how they know. if we talk about our time of childhood that time ,we tried other option to engage or by our parents ,they gave time to teach or play wid us.

Ankur apart from all this things you can try putting a note on mobile if he can reads ...like
Mere ko koi aagar 10 minute se jayeda dekhta hai toh mujhe aacha nahi lagta...
This might sound silly but it actually works.
Best way is to divert his mind from mobile and dont use mobile infront of him.
Secondly when ever he takes mobile ask him to put it back.
If he denies ask him aap isko 5 min dekh ke rakhoge,he will instantly say yes... and it might turn surprise to you he might keep mobile